[LTP] [PATCH 2/2] Add test for CVE 2021-38198

[Richard Palethorpe]

Hello,

Martin Doucha <mdoucha@suse.cz> writes:

> On 15. 03. 22 15:19, Richard Palethorpe wrote:
>> Hi Martin,
>> 
>> Martin Doucha <mdoucha@suse.cz> writes:
>>> +	if (isdigit(buf[0])) {
>>> +		sscanf(buf, "%d", &ret);
>> 
>> checkpatch complains that the return value is not checked. Also it wants
>> you to use tst_parse_int.
>
> if (isdigit()) above ensures that the return value does not matter. But
> I'll change it to tst_parse_int() in v2.
>
>>> +static void disable_tdp(void)
>>> +{
>>> +	if (!access(TDP_MMU_SYSFILE, F_OK)) {
>>> +		/* FIXME: Is this sufficient to disable TDP? */
>> 
>> What happens if this doesn't work and TDP is enabled? I seem to have it
>> enabled and the test still passes even if I comment out the call
>> to disable_tdp.
>> 
>> I'm wondering whether it will be easy to tell if a test failure is due
>> to TDP or if it can result in silent false negatives?
>
> AFAIK, the kernel bug was fixed before the tdp_mmu sysfile was
> introduced.

Ah I see TDP is very new https://lwn.net/Articles/832835/

> So somebody will have to revert the fix and run the test on
> custom kernel to answer that question.

Did you reproduce the bug?

I could try this next week.

>
> The bug is not reproducible with TDP enabled.
>
>>> +	.save_restore = (const char *const []) {
>>> +		"?/sys/module/kvm/parameters/tdp_mmu",
>> 
>> This needs updating to use struct tst_path_val.
>
> Yes, the patch was sent before the .save_restore structure was changed.


-- 
Thank you,
Richard.